1. Field of the Invention
This invention relates to an improved miniature impact tool of the type which is a hand-held mechanically operated tool for use in engraving and other applications, and more particularly to such a tool in which an improved mechanism is provided for delivery of intermittent force impulses to a chisel engraving tool.
2. Background Art
My previous patents, U.S. Pat. No. 4,030,556 and U.S. Pat. No. 5,449,044, and my copending application Ser. No. 08/846,888 (U.S. Pat. No. 5,803,183) describe a miniature tool that is particularly suited for applications such as engraving, chipping, die making, dental and orthopaedic surgery, sculpting, carving, riveting, etc. This is a hand-held impact tool in which rotary motion is converted to linear motion wherein intermittent force is applied to a striker causing it to impact on (contact) a chisel tool held in contact with a workpiece. A drive portion of the miniature tool converts rotary motion to linear motion by means of a cam interface. A spring and plunger arrangement is used to provide the intermittent force which is delivered to a striker that contacts a chisel tool holder. Due to the compressive force of the spring, the striker will provide a sharp blow to the tool holder causing the tool to chip or carve or otherwise impact on the intended workpiece. This cycle is continually repeated as the cam is caused to rotate against a bearing surface connected to the striker.
The entire contents of U.S. Pat. Nos. 4,030,556 and 5,449,044 and copending application Ser. No. 08/846,888 are incorporated herein by reference. Pertinent portions thereof will also be reviewed in the description of the preferred embodiments of this invention.
Copending application Ser. No. 08/846,888 is based on a recognition of a potential problem in a portion of the miniature impact tool of my previous U.S. Pat. Nos. 4,030,556 and 5,449,044. Based on my experimentation and use of this impact tool, I had found that the spring plunger assembly used to provide force impulses to a hammer (or striker) did not always provide impulses having approximately constant (uniform) amplitudes. Further, the screw type adjustments used to provide force impulses of different amplitude did not, for reasons of vibration and wear, work well to maintain the magnitude of the applied impact force. In turn, this affects the speed with which engraving can be done and the reproducibility of repeated engraving operations. It may also adversely affect the precision of the engraving.
I have now found that when the tool is over speeded a problem can occur which will cause damage to the cam surface and other components used to convert rotary motion to linear motion of the striker. In turn, this will limit the useful life of the tool and will necessitate a repair. My present invention addresses this situation.
Accordingly, it is a primary object of this invention to provide a miniature impact tool of the general type described in my previous U.S. Pat. Nos. 4,030,556 and 5,449,044 and in copending application Ser. No. 08/846,888 in which the assembly providing intermittent force impulses is improved.
It is another object of this invention to provide an improved tool of the general type described in my cited U.S. patents and copending application Ser. No. 08/846,888 which achieves more reliable and precise engraving under various conditions of tool operation.
It is another object of this invention to provide an improved tool of the type described in my above cited patents and copending application in which the features of compactness, light weight, and ability to be hand-held are maintained while providing an efficient tool that delivers intermittent force impulses of a predetermined magnitude over extended periods of use.
It is another object of this invention to provide a miniature impact tool of the general type described in my above cited U.S. patents and copending application that is more tolerant of an over speeding condition in the use of the tool.